Oceans cover two-thirds of the planet's surface but remain data-sparse regions for weather and climate observations for obvious logistical reasons. Relatively little is known about marine precipitation mechanisms, although their impact on civilization through climate energetics and land-falling coastal storms may be very large. Temporary deployments of Doppler radars on research ships have been conducted for field campaigns in the past. A new tool for oceanic precipitation observations is the 5.6-GHz (C-band) Doppler radar on board the NOAA research vessel, Ronald H. Brown (RHB). The RHB is among the world's most technologically advanced seagoing research platforms and is the only ship in the U.S. civilian fleet to carry Doppler radar. The new radar complements a suite of existing oceanographic and atmospheric remote and in situ sensors routinely operated onboard. In many respects, the radar is the equivalent of an oceangoing NEXRAD that can provide research-quality observations, in addition to routine storm surveillance, beyond the reach of land-based radar netoworks. The radar's beam is motion-stabilized by the use of an inertial navigation system which monitors the instantaneous ship attitude and adjusts the antenna to maintain the desired earth-relative elevation and azimuth angles. This allows the radar to provide accurate Doppler velocity data even in rough seas. This article will discuss the operating characteristics, basic capabilities, and applications of this unique research system. Initial uses of the radar include studies of monsoon rainfall, deep tropical convection, climate-change-related aspects of marine equatorial conditions, and validation of satellite-based rain algorithms. The RHB provides a modern, top-quality seagoing platform, complete with Doppler radar, for research beyond the confines of land.